1. Field of the Invention
The present invention relates to an optical information reading apparatus for reading optical information, such as, bar code and/or two-dimensional information, presented on a recording medium or a read object.
2. Description of the Prior Art
Optical information reading apparatuses are known as shown, for example, in FIGS. 11(A) and 11(B). FIG. 11(A) shows the internal structure of a hand-held optical information reading apparatus 30 and FIG. 11(B) shows a bar code label 6 being read by optical information reading apparatus 30. Optical information reading apparatus 30 includes a light source 8 for emitting light to impinge on bar code label 6 having bar code 2 and optically readable characters (hereinafter also referred to as "OCR characters") 4 printed thereon, and an optical system 14 including a reflecting mirror 10 for receiving the light reflected from bar code label 6 and a condenser lens 12 for collecting the reflected light from the reflecting mirror 10 and forming an information image of the bar code label 6. The optical information reading apparatus 30 further includes a traditional image sensor 16 arranged to capture the formed information image of the bar code label 6, an electronic circuit substrate 18 provided with a signal processing circuit for processing the captured information image of the bar code label 6 to decode the bar code 2 and the OCR characters 4, and a hand-held housing 20 which accommodates the foregoing elements as a unit.
As shown in FIG. 12(A), the signal processing circuit on the electronic circuit substrate 18 includes an amplifying circuit 110 for amplifying weak analog image signals output from the image sensor 16, a digitizing circuit 112 for converting the amplified analog image signals into digital data, i.e. binary data, and an OCR character decoding circuit 114 for decoding the OCR characters 4 contained in the information image from the binary image signals output from the digitizing circuit 112. The signal processing circuit also includes a counting circuit 116 for measuring widths of bars and spaces of the bar code 2 contained in the binary image signals output from the digitizing circuit 112 corresponding to one horizontal scanning of the image sensor 16. The signal processing circuit further includes a bar code decoding circuit 118 for decoding the bar code 2 based on output signals from the counting circuit 116, and a selecting circuit 122 for activating one of the OCR character decoding circuit 114 of the bar code decoding circuit 118 in response to a switching signal a user-operated selector switch (not shown). The selected circuit 122 outputs the result of the activated circuit via an output terminal 120 to an external circuit. A power circuit (not shown) is further provided on the electronic circuit substrate 18 to supply power to the foregoing circuits.
In general, the OCR character decoding circuit 114 identifies a character using a known pattern matching method. Specifically, the OCR character decoding circuit 114 identifies a character when a pattern of the OCR character contained in the information image matches one of a plurality of prestored basic character patterns. Further, in general, the OCR character decoding circuit 114, the counting circuit 116, the bar code decoding circuit 118 and the selecting circuit 122 are realized entirely or in part as elements of a microcomputer having, such as, a CPU, a ROM and a RAM.
Since the optical information reading apparatus 30 includes OCR character decoding circuit 114 and bar code decoding circuit 118, it can read not only the bar code 2 but also the OCR characters 4 attached to the bar code 2, and thus can also read characters printed on other media.
Accordingly, the optical information reading apparatus 30 has a wider range of applications than a normal bar code reading apparatus for reading only the bar code 2. Further, the bar code 2 is dirty and the optical information reading apparatus 30 is unable to read the bar code 2, the necessary information can be read from the bar code label 6 by reading the OCR characters 4 attached to the bar code 2.
However, to ensure that the level of accuracy for the conventional optical information reading apparatus 30 is as high as that of a bar code reading apparatus for reading only the bar code 2, an expensive two-dimensional image pickup apparatus, such as, an image pickup apparatus for HDTV high-definition television), having a large number of picture elements, particularly in the horizontal direction, should be employed as the image sensor 16, or a line sensor for reading the bar code 2 should be provided within or separately from the image sensor 16.
Specifically, as shown in FIG. 12(B), a two-dimensional image sensor 16 may be formed by arranging a large number of photoelectric conversion elements (picture elements), such as CCDs, in longitudinal and transverse directions. If an inexpensive two-dimensional image pickup apparatus having some hundreds of picture elements arranged in the horizontal direction is employed as the image sensor 16, OCR characters 4 can be decoded, but difficulty is likely to be encountered in decoding the bar code 2. Specifically, since the OCR characters 4 can be decoded using the pattern matching method described above and further since the OCR characters 4 can be arranged in a less delicate manner than the bar arrangement of the bar code 2, the image of the OCR characters 4 can be decodably captured without difficulty even by the foregoing inexpensive image pickup apparatus. 0n the other hand, for decoding the bar code 2, lengths of and spaces in a horizontal scanning direction should be measured precisely. However, the foregoing inexpensive image pickup apparatus is unable to provide an image resolution necessary for precisely measuring small scale bar code lengths and decoding such a bar code. Accordingly, in order to ensure a reading accuracy for the bar code 2 as high as that provided by the bar code reading apparatus for reading only the bar code 2, a line sensor having some thousands of photoelectric conversion elements in line, which has been used in conventional bar code reader, should be provided within or separately from the image sensor 16 for reading the bar code 2, or an expensive two-dimensional image pickup apparatus, such as an image pickup apparatus for HDTV, having some thousands of picture elements in the horizontal direction, should be employed as the image sensor 16.
The foregoing problems are not limited to the optical information readers for reading bar code and OCR characters but also apply to optical information reader for reading bar code and two-dimensional code such as a so-called matrix code (for example, Data Code and Veri Code) which is formed by white and black cells arranged in a matrix, or a so-called stacked bar code (for example, PDF417) which includes bar code-like data in a stacked fashion.
These two-dimensional codes are disclosed and introduced, for example, in Japanese First (unexamined) Patent Publication No. 2-12579 and in the journal "Bar Code" (vol. 1993-11 published by Japan Industrial Publishing Co., Ltd.).
In order to compensate for an insufficient number of picture elements in an image sensor, it has been proposed to increase the apparent number of picture elements by mechanically vibrating the image sensor to capture multiple images, and synthesizing the captured images. However, since the image sensor itself is mechanically vibrated, durability is reached. Accordingly, the proposed method is not desirable, particularly for hand-held optical information readers.